As the material for producing various cans, particularly cans for food and beverage preservation, tin-plate has been most commonly used. However, in recent years, the tin source in the world has been in short supply, and the production cost of tin-plate has been increasing. In order to solve the situation, various efforts have been made, including reduction of the coating amount of tin on electrolytic tin-plate, and developments of tin-free steel (T.F.S.) coated with metallic chromium and a chromate film thereon. Further, along with the above efforts, trials and proposals have been made to use a cold rolled steel sheet for the cans for the purposes of lowering the production cost thus saving the material source and energy, and solving the pollution caused by the used cans.
Meanwhile, in the field of the can making techniques, considerable technical progress has been made and it is now possible to produce cans by the drawing and redrawing process or by the drawing and ironing process. In the production of DrD or DI cans, the starting steel sheet material (black plate) is deep-drawn (DrD), further ironing flanged, and coated on both inside and outside surfaces, and then after charging with foods or beverage, the lid is set. According to the above production method, thin two-piece cans having high strength can be obtained, and various advantages are provided, including the labour-saving by automation of the process line and the cost-saving.
However, the above production method requires a high level of formability of the starting material, and thus is limited in its application in respect with formability and corrosion resistance. Therefore, up to now only aluminum and tin-plate have been successfully formed by the above method, and the tin-free steel or cold rolled steel sheet has never been successfully formed into cans by the above method. If a cold rolled steel sheet can be used as the starting material for production of DI cans, this would offer a tremendous advantage and solve the world-wide problem of the tin source.